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Since I do not do 'zoning', but always want to learn something new, can anyone explain, simply, the use of the bypass & barometric dampers to me.
On the bypass damper, what are you bypassing and where do you bypass it to. ( I assume, the evap. air flow )
Where would the barometric damper be located & what controls the degree of open or close ??

with bypass dampers you are moving excess air that you don't need going into other areas of the home. you re-route it (hence bypass) into other non-needed areas, (like the utility room, some to the return air, some to the basement) basically, whatever the excess is, you can reduce the strain on the equipment by using these. the barometric dampers that i use have weight adjustments that you set according to whatever static pressure that you are trying to maintain. if you start to build pressure they open to some degree and then fluctuate right along with the amount of pressure buildup. if you use zoning, which in my opinion is a great thing to offer, you need to understand and use these items. hope this helps you out.

Good question. Both are essentially the same thing. They bypass air from the supply back to the return. There are varying degrees of thought as to whether it necessary to do this. Some manufactuers say it is essential, EWC for instance, basically you must do something with the air that is going to be supplied to the supply register(s). For example, if you have a four ton that is broken up into two zones (kiss...keep it simple) you do not want to supply one zone with four tons of air. So you bypass that air. As far as controls, it can vary, some do it with weighted dampers, some with an actual static pressure control, which is more accurate. A little more difficult to set up but you have better results. The benefits can vary depending on the sysytem, but they work great with heat pumps, as you can create a "hot heat pump", think about bypassing air from the supply back into the return. You raise the return temp. and the supply temp must go up, it shortens the cycle time down some, but it can give you up to 130 degree+ supply sir from a heat pump. Zoning is great if done properly, but unfortunately in our industry too many hack have tried it and the results speak for themselves. Your car has zoning, your electricity is zoned in your home, so is your plumbing, but why is it that your hvac system is not? I hope this helps, and has answered your questions.

The reason most zoning manufacturers talk about bypassing air is to eliminate objectionable air noise. If you have a zone which is small, and it is the only zone calling for service, the capacity of your blower may cause noise issues. There is less need for a bypass when you have zones of equal size. In any event the issue should always be based on the homeowners perception. What may be objectionable to you may or may not be to the homeowner. Over bypassing (too large a Bypass Damper ) creates more problems in a system than under bypassing. Make certain you go to a manufacturers chart and properly calculate your needs. In any event the key is make certain that if you have a bypass installed in your return keep it as far down the supply as possible but before you start seeing any restrictions in that trunk.
It is a good idea to have a leaving air temperature sensor as a feature of your system if you are installing a bypass. Free zones (runs without dampers) are a possible solution if there are areas within the home which will not become overconditioned with the extra service. Bypass technology and theory has evolved greatly in the last few years. You should not let a bypass be an impediment to providing comfort to your customer.

Freeze stats for when evaporator temps. become low enough to freeze the coil in the cooling cycle? What are the high pressure switches rated at when supply air is recirculated in the heating cycle? What happens when the filter gets dirty, AND hot supply air is being recirculated? It seems like a good way to shorten equipment life to me. Flame away zoners, I've just never been an advocate.

There is nothing more frightful than ignorance in action....Mark Twain

Originally posted by HVAC Pro Freeze stats for when evaporator temps. become low enough to freeze the coil in the cooling cycle? What are the high pressure switches rated at when supply air is recirculated in the heating cycle? What happens when the filter gets dirty, AND hot supply air is being recirculated? It seems like a good way to shorten equipment life to me. Flame away zoners, I've just never been an advocate.

I forget but you can look at honeywells zoning equipment at the honeywell site...all the installation documents are there...in pdf.

I think on the honeywell system you have a choice of 40 or 48 degree leaving temperature low limit in cooling and a choice of anywhere between 110 and 160 leaving temperature in heating.....there is a sensor you install in the supply.

I dont see any problems with life expectancy in cooling as far as controls and transformers are concerned but I have seen heat contactors worked a bit in heating on zone systems where some of the zones were small.....